Falsification tests of climate theories
Is the recent warming of Greenland unprecedented?
or, Come for a ride on my polar roller-coaster
The strongest reasons for doubting the man-made global warming hypothesis come from pre-industrial climate change. During the past 10,000 years, since soon after the end of the last ice age, there have been bigger ups and downs in global temperatures than during the 20th Century. Yet according to the IPCC, citing measurements of gas trapped in polar ice, the concentration of CO2 varied by only about 20 ppm throughout those 10,000 years – less than a quarter of the change during the 20th Century.
So whatever caused the pre-industrial climate changes, it was not CO2. The record is well accounted for, in fact, by (1) a change in the Earth’s attitude in orbit, which brought a gradual cooling to the Northern Hemisphere, and (2) solar variations that superimposed on that trend a succession of warmings and coolings. Yet to offer such natural explanations for past events does not logically falsify the man-made global warming hypothesis, because its supporters say it represents an important new factor in climate change.
If increasing CO2 had no effect whatever on the climate, that might be surprising, but the claim of the hypothesis and its computer models is that the new contribution from man-made greenhouse gases has become the main driver of recent climate change. Implied here is a falsifiable statement, namely that there is something very unusual about the recent warming of the world. That is certainly the sense of many scientific and political pronouncements about global warming.